In a manufacturing process of a three-dimensionally stacked memory, a stacked film of silicon oxide films and silicon nitride films is formed on a wafer, trenches penetrating the stacked film are formed, and thereafter a chemical liquid is brought into contact with the silicon nitride films through the trenches to remove the silicon nitride films selectively from the stacked film. Subsequently, to form word lines, a CVD method using material gas is performed to form tungsten films inside cavities in respective layers from which the silicon nitride films have been removed.
The tungsten films are formed not only inside the cavities in the respective layers but also on the sidewalls of the trenches communicated with the cavities. The tungsten films on the sidewalls of the trenches are continuous with the tungsten films in the cavities of upper layers and the tungsten films in the cavities of lower layers, respectively. If the tungsten films remain continuous with one another, upper and lower word lines mutually short-circuit. Accordingly, to isolate the upper and lower word lines electrically, the tungsten films on the sidewalls of the trenches are removed by etching.
Conventionally, a time point at which a predetermined time has elapsed from start of film formation is used as an end point of the film formation. In some cases, a difference in film-formation rates of the tungsten films is generated between when the cavities remain opened, that is, when the surface area of the stacked film is large and when the cavities are blocked, that is, when the surface area of the stacked film is small. Under this premise, when the shapes of the openings of the cavities are non-uniform among different wafers (lots), the film thicknesses of the tungsten films on the sidewalls of the trenches are also non-uniform at an end point of film formation. When the film thicknesses of the tungsten films on the sidewalls of the trenches are non-uniform, etching conditions of the tungsten films on the sidewalls of the trenches cannot be uniformed among wafers. Accordingly, the manufacturing efficiency becomes poor.
Furthermore, conventionally, the flow rate of material gas is kept constant from start to an end point of film formation. For this reason, after the openings of the cavities are blocked by the tungsten films, an excessive amount of material gas is supplied until the end point of film formation. Accordingly, the economic efficiency becomes poor.
Therefore, in manufacturing semiconductor devices, improvement in manufacturing efficiency and economical efficiency has been demanded.